Medication delivery pens are hypodermic syringes used for self-injection of precisely measured doses of medication. Pens are widely used, for example, by diabetics to self-inject insulin. A typical prior art medication delivery pen includes a cartridge which contains a volume of liquid medication sufficient for several doses. The dose is injected into a tissue area, such as the intramuscular tissue layer, the subcutaneous tissue layer, or the intradermal tissue layer.
The assembly and operation of a typical pen injection device is described in commonly-assigned U.S. Pat. No. 7,645,264, issued on Jan. 12, 2010, which is incorporated herein by reference in its entirety.
Pen injection devices, such as the exemplary pen injector 50, as shown in FIGS. 1 and 2, typically comprise a dose knob/button 24, an outer sleeve 13, and a cap 21. The dose knob/button 24 allows a user to set the dosage of medication to be injected. The outer sleeve 13 is gripped by the user when injecting medication. The cap 21 is employed by the user to securely hold the pen injector 50 in a shirt pocket, purse, or other suitable location.
FIG. 2 is an exploded view of the exemplary drug delivery pen 50 shown in FIG. 1. The dose knob/button 24 has a dual purpose and is used to both set the dosage of the medication to be injected and to inject the dosed medicament via a lead screw 7 and stopper 15 from a medicament cartridge 12, which is attached to the drug delivery pen through a lower housing 17. The lower housing 17 typically has dosage indicia on the exterior thereof. The medicament cartridge 12 is typically a glass tube sealed at one end with a septum 16 and at the other end with the stopper 15. In standard drug delivery pens, the dosing and delivery mechanisms are all found within the outer sleeve 13. Those mechanisms are not described in greater detail here as they are understood by those knowledgeable of the art.
A pen needle assembly 10 (hereinafter referred to as pen needle 10 for brevity) includes a hub 20, a patient needle 11 extending from a patient end of the pen needle, and a septum-penetrating needle cannula 18 disposed within the hub 20 on a non-patient side thereof. The septum-penetrating needle cannula 18 is in fluid communication with the patient needle 11. The hub 20 is preferably screwed onto the lower housing 17. In attaching the hub 20 to the lower housing 17, the septum-penetrating cannula 18 pierces the septum 16, but the septum 16 does not move with respect to the medicament cartridge 12. The stopper 15, however, is axially displaceable within the medicament cartridge 12 while maintaining a fluid tight seal. The distal movement of the plunger or stopper 15 within the medicament cartridge 12 (due to advancement of the lead screw 7) causes medication to be forced into the patient needle 11 of the hub 20.
To protect a user, or anyone who handles the pen needle assembly 10, an outer shield 29, which attaches to the hub 20, covers the hub 20. The outer shield 29 can also be used as a handle or grip to screw hub 20 onto or off pen injector 50. An inner shield 28 covers the patient needle 11 within the outer shield 29. The inner shield 28 can be secured to the hub 20 to cover the patient needle 11 by any suitable means, such as an interference fit or a snap fit. The outer shield 29 and inner shield 28 are removed prior to use. The cap 21 fits snugly against outer sleeve 13 to allow a user to securely carry the pen injection device 50.
A pen injector, such as pen injector 50, can be designed to have the shortest length possible, or it can be designed to protect a pen needle 10 that has already been assembled to the pen injector 50. While it is highly desirable to produce the shortest, smallest pen possible, there are times when a user might want to pre-assemble a pen needle 10 to a pen injector. For example, a user may be going to a restaurant to eat and may need to provide an injection of very fast acting insulin just prior to eating. When timed properly, such an injection provides a more consistent glucose level. But the injection cannot be given too far in advance because the user's glucose level will drop too much. This situation effectively requires that the injection be given at the restaurant. For convenience, the user may wish to pre-assemble the pen needle 10 with the pen injector so that it is ready to use. If the pen injector 50 is designed to protect an assembled pen needle 10 within the cap 21 when the pen needle 10 is not assembled with the pen injector 50, the pen injector 50 is longer than it needs to be, and thus takes up more space. What is needed is a pen injector that can accomplish both modalities, one in which the pen injector is as small as possible, and one in which a pen needle can be accommodated while assembled to the pen injector.